Simon Wong opened SPR-15895 and commented

When I set the SimpleAsyncTaskExecutor setConcurrencyLimit with value ConcurrencyThrottleSupport.NO_CONCURRENCY (i.e. value = 0), the execute of SimpleAsyncTaskExecutor will not take NO_CONCURRENCY in consideration. The Runnable will always be executed in all cases.

public void execute(Runnable task, long startTimeout) {
     Assert.notNull(task, "Runnable must not be null");
     Runnable taskToUse = (this.taskDecorator != null ? this.taskDecorator.decorate(task) : task);
     if (isThrottleActive() && startTimeout > TIMEOUT_IMMEDIATE) {
          this.concurrencyThrottle.beforeAccess();
          doExecute(new ConcurrencyThrottlingRunnable(taskToUse));
     }
     else {
          doExecute(taskToUse);
     }
}

The root cause is isThrottleActive() will always returns false as the concurrent limit = 0 in this case, hence ConcurrencyThrottleAdapter will not be processed.

This is also the reason why the 1st test case SimpleAsyncTaskExecutorTests cannotExecuteWhenConcurrencyIsSwitchedOff is disabled by the SPF committer.

The current workaround is SimpleAsyncTaskExecutor.setConcurrencyLimit(1).

BTW, NO_CONCURRENCY = 0 is somehow wrong in definition. No currency should means there should be one invocation of method at a time, other invocations should be waited. That means NO_CONCURRENCY should have a value of 1 instead.

Affects: 4.3.10

Issue Links:

• Migrate remaining JUnit 3 based tests to JUnit 4 [SPR-13514] #18091 Migrate remaining JUnit 3 based tests to JUnit 4

Referenced from: commits f3a2f57, 204ddeb